The present disclosure relates, in various exemplary embodiments, to ink jet ink compositions and ink jet ink sets. Specifically, the present exemplary embodiments relate to ink compositions in an ink jet ink set that are designed to reduce intercolor bleed when the inks are printed onto a substrate.
Ink jet printing is a non-impact printing method that produces droplets that are deposited on a print substrate (recording medium) such as plain paper, coated paper, transparent film (transparency), textile, or the like, in response to electronic digital signals. For example, thermal or bubble jet drop-on-demand ink jet printers have found broad applications as output for personal computers in the office and at home.
In existing thermal ink jet printing processes, the printhead typically comprises one or more ink jet ejectors, each ejector includes a channel communicating with an ink supply chamber, or manifold, at one end and having an opening at an opposite end, referred to as a nozzle. A thermal energy generator, usually a resistor, is located in each of the-channels at a predetermined distance from the nozzles. The resistors are individually addressed with a current pulse to momentarily vaporize the ink within each respective channel to form a bubble that expels an ink droplet. As the bubble grows, the ink rapidly bulges from the nozzle and is momentarily contained by the surface tension of the ink as a meniscus. This is a very temporary phenomenon, and the ink is quickly propelled toward a print sheet. As the bubble begins to collapse, the ink remaining in the channel between the nozzle and the bubble starts to move toward the collapsing bubble, causing volumetric contraction of the ink at the nozzle resulting in the separation of the bulging ink from the nozzle as a droplet. The acceleration of the ink out of the nozzle while the bubble is growing provides sufficient momentum and velocity to propel the ink droplet in a substantially straight line direction towards a print substrate, such as a piece of paper. Subsequently, the ink channel refills by capillary action and is ready for the next repeating thermal ink jet process. Thermal ink jet processes are well known and described in, for example, U.S. Pat. Nos. 4,251,824, 4,410,889, 4,412,224, 4,463,359, 4,532,530, 4,601,777, 5,139,574, 5,145,518, and 5,281,261, the entire disclosures of which are incorporated herein by reference. Because the droplet of ink is emitted only when the resistor is actuated, this type of thermal ink jet printing is known as “drop-on-demand” printing. Other types of drop-on-demand printing such as piezoelectric ink jet printing and acoustic ink jet printing are also known.
Continuous ink jet printing is also known. In continuous ink jet printing systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. Multiple orifices or nozzles can be used to increase imaging speed and throughput. The ink is perturbed while being ejected from an orifice, causing the ink to break up into droplets at a fixed distance from the orifice. At the point of break-up, the electrically charged ink droplets pass through an applied electrode that switches on and off in accordance with digital data signals. Charged ink droplets pass through a controllable electric field that adjusts the trajectory of each ink droplet in order to direct it to either a gutter for ink deletion and recirculation or to a specific location on a recording substrate to create images.
In an ink jet printing apparatus, the printhead typically comprises a linear array of ejectors, and the printhead moves relative to the surface of the print substrate, either by moving the print substrate relative to a stationary printhead, or vice-versa, or both. In some types of apparatuses, at least a relatively small print head supplied with an ink moves across a print sheet numerous times in swaths in order to complete an image. For multicolor ink jet printing, a set of printheads and ink (e.g., cyan, magenta, yellow and black) can move across the print substrate numerous times in swathes and disperse selected inks in any desired pattern (e.g., ⅛, ¼, ½, fulltone (1/1)) according to digital signals. The speed of this type of single or multiple color ink jet printing on a substrate is determined by the moving speed of the printheads across the print substrate, ink jetting frequency (or frequency response), and the desired number of swathes needed for printing. The printing speed of this type of ink jet apparatus can be increased if two or more print heads are budded together to form a partial-width array printhead for printing each ink in a monochrome or multicolor ink jet printing system. The partial-width ink jet printhead has more ink jet nozzles per printhead, and can deliver a large number of ink droplets across the substrate in a swath in a short period of time. Monochrome or multicolor ink jet printing apparatuses using one or several partial-width printheads may have a faster printing speed than current commercial ink jet printers.
Alternatively, a printhead that consists of an array of ejectors (e.g., several butted printheads to give a full-width array printhead) and extends the full width of the print substrate may pass an ink down once onto the print substrate to give full-page images, in what is known as a “full-width array printer”. When the printhead and the print substrate are moved relative to each other, image-wise digital data is used to selectively activate the thermal energy generators in the ink jet printhead over time so that the desired image will be created on the print substrate at a fast speed. For multicolor ink jet printing, several full-width array printheads and inks (e.g., cyan, magenta, yellow, and black) can be used to deliver multiple color inks onto a print sheet. This type of multicolor ink jet printing process is capable of printing multiple color images and monochrome color images on a print substrate at a much faster speed (e.g., more than five pages of full color images per minute) than current commercial color ink jet printers.
In multicolor ink jet printing processes, several inks can be printed on a print substrate. In some instances, two different inks can be printed next to each other or one ink is printed on top of the other ink(s). Intercolor bleed can occur if the inks are not dried properly or if the printing process is too fast for the inks to set. Undesired ink mixing on a print substrate, especially on the surface of a plain paper, can cause distorted images near the border of two inks. After the inks dry, the border of the two inks can appear irregular with poor edge sharpness (or raggedness) due to the invasion of one ink into the other. Such bleed images are visibly unattractive. This phenomenon is generally called intercolor bleed. Intercolor bleed occurs particularly when a darker colored ink (such as a black ink) and a lighter colored ink (such as a yellow ink, a cyan ink, a magenta ink, or the like) are printed next to each other or on top of each other, because of the high contrast between the two colors. Intercolor bleed can also occur when two color inks are printed next to each other or on top of each other (for example yellow ink next to magenta ink, yellow ink next to cyan ink, magenta ink next to cyan ink or the like). The severity of the intercolor bleed generally is affected by the type and composition of the ink, absorption rate of the printer substrate, printhead design, ink drop mass, ink dot size and method and speed of printing. As a result, there is a need to reduce intercolor bleed and to produce high quality multicolor ink jet images on print substrates, including plain and coated papers, transparencies, textiles and other desired substrates.
Further, although carbon black inks are capable of producing good quality black images on North American and Japanese plain paper, they are not used as mainline black inks in multicolor printing process because they have tendency to exhibit poor intercolor bleed performance when printed next to color inks. The poor intercolor bleed performance of such inks is especially evident when such inks are printed next to yellow colored inks due to the high level of color contrast. In addition, although other black inks exhibit suitable intercolor bleed performance, these inks exhibit poor mid frequency line edge noise (MFLEN) data on Japanese paper.
Therefore, there remains a need for improved multicolor thermal ink jet printing processes. In addition, a need-remains for multicolor thermal ink jet printing processes wherein the print generated exhibits reduced intercolor bleed. Further, a need remains for multicolor thermal ink jet printing processes wherein the prints generated exhibit excellent image quality. In particular, there is an urgent need for an ink (especially a color ink) that provides good MFLEN (mid frequency line edge noise) and intercolor bleed performance when printed together with black inks to form multicolor images.
Attempts to reduce or eliminate intercolor bleed in ink jet printing processes typically involve the use of anti-intercolor bleed agents in the ink compositions. These agents are generally added to the color vehicle to “crash” the stability of the carbon black dispersion. The anti-intercolor bleed agent is often a salt. High levels of salt, however, are generally required to achieve the print quality latitude across a wide paper set. At high levels of salt, jetting, which is a key consideration in ink design, is degraded.
Therefore, there is also a need to provide both black and color ink jet ink compositions that do not require conventional anti-intercolor bleed agents but, when printed on a substrate, exhibit reduced intercolor bleed. Additionally, there is a need for an ink jet printing process employing such compositions. There is also a need to reduce the secondary color mottle, that is, to reduce the spotty or uneven appearance in the printing of secondary colors (e.g., green, red, etc.).